1. Field of the Invention
The present invention relates to a method of mounting an optical device having a step on an outer profile of an element on a substrate by face down bonding and a mounting structure. The present invention more particularly relates to an optical integrated module device mounting an optical device by the mounting method and the mounting structure described above and an optical device such as an integrated optical head device using the same.
2. Related Art
A nitride semiconductor laser device capable of oscillating a blue laser light at a wavelength of about 410 nm has the following constitution. That is, a nitride semiconductor material comprising InGaN as an active layer and AlGaN as a clad layer are crystallographically grown on a gallium nitride (GaN) substrate by a crystal growing method
When such a blue semiconductor laser is put to practical use, the recording capacity of existent DVD apparatus using red laser light at a wavelength of about 650 nm will be increased by about four times. In view of the foregoing, sooner practical use of the blue semiconductor laser is expected. However, since no GaN substrate of a large diameter is available, crystal growth is conducted by using a sapphire (Al2O3) substrate having a lattice constant substantially identical with that of the GaN substrate. A typical example of an optical device having a step on the outer profile of the element is the GaN series semiconductor laser element. Accordingly, a P-electrode and N-electrode of a GaN series semiconductor laser formed on sapphire as an insulator are formed on one identical surface, while the P-electrode on the side of the active layer is made higher than the N-electrode, for example, by about 3 μm. For the purpose of improving the characteristic and the life of the optical device, mounting is preferably conducted by the face-down bonding. In this case, however, it is necessary to mount the device with the surface having the step on the outer profile of the element being opposed to the element mounting substrate. Accordingly, for the sake of electrically connecting the P-electrode and the N-electrode having a step on the outer profile of the element as in the existent GaN series semiconductor laser element, a mounting method different from the prior art is required. That is, in most of existent elements, the P-electrode or N-electrode can be formed on one of the surface and rear face of the outer profile of the element. Accordingly, there was no problem that occurs in the nitride semiconductor laser device formed on an insulative substrate.
FIG. 7 is a cross sectional view illustrating an example of mounting a gallium nitride series semiconductor laser element on a substrate. A laser diode chip 108 has a structure in which a gallium nitride series compound semiconductor layer 102 is laminated on the sapphire substrate 101. In the laser diode chip 108, a positive electrode 104 and a negative electrode 103 are formed on one identical surface of a crystal laminate. Then, as can be seen from FIG. 7, the outer profile of the optical device has a step, and the positive electrode 104 and the negative electrode 103 are formed on the surfaces of different levels that form the step.
On the other hand, an insulative heat sink 105 is formed with a positive electrode 106 and a negative electrode 107 being metallized on one identical surface of the heat sink. Each of the electrodes on the heat sink and each of the electrodes 104, 103 of the laser diode chip 103 corresponding to them respectively are connected with each other. Such a connection method is referred to as mounting by face down (also referred to as junction down) bonding since connection is made such that the heat sink 105 is covered not on the side of the crystal growing substrate but at the junction surface constituting the active layer of the laser diode chip 108. Reference numeral 109 denotes connection solder. Such a constitution is disclosed in, for example, Japanese Patent Laid-Open No. Hei 7-235729.